This invention relates to a device for indicating the position of a gearshift lever, particularly for use with commercial or industrial vehicle transmissions having five or more forward speeds.
The invention is particularly applicable to tractor-trailers or other vehicles having anywhere from five to fifteen speed transmissions. Very often a driver of such a vehicle has no way of rapidly and accurately determining which gear is engaged. This is particularly troublesome in units having two or more gear ranges (such as high/low or overdrive) since one gearshift position may represent two or three different gears. Thus, for example in a unit having low, direct and high ranges, the first gearshift position may represent gears 1, 6 and 11. Also, when the vehicle is being operated at night, the gearshift position can be difficult to determine in the dark.
If, for example, the driver attempts to start off and thinks, by looking at the main gearshift lever, that he is in first gear, when in fact he is in gear six or gear eleven, the drive train could be damaged due to excessive torque being applied to both the clutch assembly and the transmission. On the other hand, if the driver is trying to downshift, such as when traversing a long downhill slope, he may think he is in a lower gear than he actually is, thus producing excessive wear on the clutch, transmission and brakes.
Devices for ascertaining the state of a gearbox are known. U.S. Pat. No. 3,943,792, issued Mar. 16, 1976 to Sibeud, for example, discloses an apparatus employing transverse bars which rest on the sliding gear selector rods of a standard gearbox. The transverse bars engage notches machined in the gear selector rods to generate signals representative of the position of the selector rods. A device of this type requires that major modification be made to the standard gearbox, including (1 ) accurately machining additional notches in the gear selector rods in a particular coded format; and (2 ) providing the gearbox with additional mechanical members, such as movable transverse bars.
The purpose of the gearshift position indicator of this invention is to provide the operator of the vehicle with a visual indication of which gear is engaged in the transmission, thereby enabling the driver to change gears in the desired manner to avoid damage to the engine, drive train, brakes, etc.
Another object of this invention is to provide a simplified mechanical construction which requires only minor modifications to a standard gearbox and is therefore economically practical.
Another object of this invention is to permit gearboxes presently in use to be easily retrofitted with the position indicator by an ordinary mechanic, which makes the addition of this invention to vehicles currently on the road further economically practical.
Briefly, the invention comprises a number of microswitches mounted on the transmission housing for engagement with the shift bars of the transmission. The microswitches are connected to a coder which generates binary coded decimal (BCD) signals representing the shift bar positions corresponding to the engaged gear in the transmission. The output of the coder drives a seven segment LED digital display unit through a decoder/driver circuit. The LED display provides a visual indication of the number of the gear engaged.